DEEP VELOCITY STRUCTURE OF RIFTED CONTINENTAL-CRUST, UNITED-STATES MID-ATLANTIC MARGIN, FROM WIDE-ANGLE REFLECTION REFRACTION DATA

We present new ocean-bottom, wide-angle seismic data, collected during the 1990 EDGE Mid-Atlantic multichannel seismic experiment, which provide a measurement of the deep velocity structure of rifted Appalachian continental crust beneath the U.S. East Coast continental margin. Reflections from the entire crust and Moho are visible from offsets of zero to 100 km. One-dimensional inverse traveltime modeling reveals a 34-km-thick crust consisting of four layers beneath the post-rift sediments, with velocities of 5.9, 6.3, 6.4, and 6.85 km/s. This velocity structure is indistinguishable from that found beneath several Appalachian terranes in the northern Appalachians of New England. The average velocity of 6.85 km/s in the lower crust limits the landward extent of the high-velocity (7.2-7.4 km/s) lower crust found farther seaward, and supports the interpretation of that layer as the result of rift-related magmatic underplating, rather than as thinned, pre-existing lower continental crust.